Yo HAPPY HOUR: [AND IT IS THAT TIME RIGHT NOW; SO, RIGHT AFTER THIS POST, I INDULGE -- MARTINI TIME.
As to your question about the mic pres on the MD-8, They are all right. You can do some nice stuff once you get the hang of the gear.
I also use the ART mic pre to "warm" up a vocal; however, I've run everything from piano to flute through the ART; it's a matter of taste and ears.
The MD-8 does a pretty good job and it's not difficult to use. Notice that the price is not dropping on MD-8's; but, wait until the MD-9 or whatever comes out, and it will, we will have a box with improved sound and it will cost more $$$; but, that's Yamaha.
Enjoy,
Green Hornet